The present invention pertains to the electrical signal simulation art and, more particularly, to apparatus for simulating the pitch, roll and azimuth signals produced by an aircraft's gyro system.
Commerical aircraft are commonly provided with multiple gyro systems. Each gyro system produces output signals corresponding to the pitch, roll and azimuth of the aircraft. These signals activate indicators within the flight deck thereby providing a visual display of pitch, roll and azimuth parameters, as well as being coupled to aircraft flight control systems, such as the autopilot. Often, redundant autopilots are employed, with each autopilot receiving input signals from redundant gyro systems. A comparator within the system monitors each gyro channel signal set, as well as the performance from each autopilot, and, in a predetermined manner, selects the appropriate one of the autopilot systems to control the aircraft.
The testing of aircraft systems which depend upon input gyro signals has been a cumbersome and expensive task. The most common approach is to remove the gyros from their aircraft mounting positions, and fasten the gyros to controlled tilt tables. By appropriate control of the tilt tables, the desired gyro test signals may be produced. Such gyro handling has often resulted in internal bearing damage to the gyro units, requiring their repair or replacement. In addition to the cost involved in repairing or replacing the gyros, there is the additional cost in man hours resulting from the time required to physically remove and then replace the gyros, as well as delays occasioned by gyro "spin up" and "spin down" times prior to handling.
Previous attempts at generating, or simulating, gyro signals have not proved successful. None of these prior attempts, for example, provided for dynamic testing of gyro responsive systems. That is, none accomplished a closed-loop test wherein commands from the control wheel and the autopilot directly deflected aircraft surfaces to simulate actual flight conditions. In addition, with systems employing multiple autopilots, no prior gyro simulation technique provided a means for offsetting the gyro signals supplied to redundant autopilots to thereby test autopilot comparator response.